Work zones and intersections are hot spots of conflict areas, leading to crashes. Though many efforts have been made to enhance the safety, there is little indication that the crashes in the two types of conflict areas are declining nationwide. Thousands of crashes are recorded every year in the United States, which are mainly attributed by the insufficiency in the traffic controls and drivers’ misjudgement. To supplement the conventional traffic controls, a smartphone based audio warning message (AWM) was proposed and tested in driving simulators regarding safety of workers in work zones as well as vehicles at intersections for left-turn. Results show that the AWM is able to effectively increase drivers’ awareness of traffic signs and dynamic traffic situations, in particular, in a hazardous situation.